Thanks for all the answers. The position could well be the problem here. I need to position it a bit higher as its located at the bottom of my open cabinet temporarily. If i go down analogue connection route is this a big step down from optical ?
A speaker is never going to sound its best in a cabinet and also being low down is not ideal either. The ideal would be to wall mount at around ear level.
The difference between analogue and digital output from the TV will depend on whch device has the better DAC for converting the signal from digital to analogue. You would have to assume the soundbar has the better DAC since it is designed for solely producing sound. That said I doubt the difference will be huge and you will probably not be able to hear it given your equipment anyway.
If it's a cabinet resonance issue, the level of control offered by such a product is far too coarse to resolve the issue, and the result of attempting to use it to reduce the boominess will likely merely make thing worse, albeit in other ways.
The best way to resolve the negative effects of having a speaker in a cabinet is to get it out of the cabinet. Electronic resolution needs fine control (equalization), not broad tone controls.